The present invention relates to a control device for an engine, particularly to a control device for an engine, which adjusts an engine torque according to an operation of an accelerator pedal performed by a driver.
JP2005-155412A discloses such a kind of art. In JP2005-155412A, a target torque of an engine is set based on a state of accelerator operation performed by a driver, and an output torque of the engine is adjusted to reach the target torque by adjusting a throttle opening and/or an ignition timing. Specifically, in this art, an output torque of an engine is adjusted such that an acceleration of a vehicle in its longitudinal direction becomes higher as a depressing speed of an accelerator pedal (i.e., a differential value of an accelerator opening) becomes higher, so as to gain an acceleration feeling and reduce vibration of the vehicle in its longitudinal direction.
Meanwhile, when traveling on a rotary, a roundabout (a circular intersection where a plurality of branch roads are connected with a circular passage, which is usually seen in Europe), or a limited speed zone where a vehicle speed is limited to be low, a driver intends to drive at a constant vehicle speed. In this case, the driver tends to operate the accelerator pedal slightly and repeatedly so as to keep the vehicle speed constant. With the conventional art, when the driver operates the accelerator pedal slightly and repeatedly as described above, the acceleration varies according to the variation of the accelerator opening. Therefore, it is difficult to keep the vehicle speed constant. In other words, with the conventional art, it is difficult to control the vehicle to maintain the constant vehicle speed.
As a solution, improving a characteristic of the acceleration in relation to an operation of an accelerator pedal, in order to easily maintain the constant vehicle speed is considered to be effective. Further, it can be said to be advantageous to suitably maintain the constant vehicle speed as described above when the accelerator pedal is operated in a state where the driver applies almost no intentional force with his/her foot when stepping on the accelerator pedal (i.e., the accelerator pedal is stepped on (depressed) with the weight of the foot itself).